How to cook sunny side up
I’VE BEEN FOOLING around with solar cooker designs for a while now.
The initial trials involved sheets of stainless-steel temporarily bent around a cast-iron Dutch oven. It seemed to work, but other things got in the way of further development.
Until now. With a spare day in hand, I marked and cut out two pieces of stainless-steel sheet to a pattern that looked something like a giant orange peel segment. Then I bent up tabs all along one side of one piece, and riveted one edge to the other sheet. A couple of triangular end-pieces completed the reflector.
A quick look through the treasure trove I have sitting under a line of trees later, I pulled out some Dexion shelf framing – it looks like oversized Meccano – and used it to knock up a frame. We were in business (see the picture at right). Or so I thought.
That particular day there was a 40-knot sou’west gale and wind chill became the dominant factor. A quick search on Google suggested that wind chill could indeed be a problem for a solar cooker, which most folk get over by wrapping the food in plastic, covering the unit with glass, or by strategic placement of windbreaks. I didn’t fancy the first idea and the last one seemed inefficient, so I drifted off to sleep pondering glass.
The next morning, the penny dropped. Sitting under the trees was the very item to solve the problem, discarded from a previous project. I once tried to heat water for an outdoor shower using a blackpainted tank in an insulated box, with a Subaru tailgate as the enclosing glass. As a water heater it was a non-starter, but the box and the tailgate might just be the perfect house for a solar cooker.
A quick hose-down, a quick hackaround of the Dexion, and there it was. It wasn’t long before I was able to sniff delicious smells wafting from the small gap above the satisfyingly-warm glass.
The focus seems quite tolerant, in that I can leave it for 20 minutes without having to shift the box to face the sun again. It’s also easy to know when you have the reflector tilted correctly as the Dutch oven is bathed in light.
If I wanted to really push things along and boil a kettle in 10 minutes, it would take more reflector area, but for what we need it does just fine. For optimal performance the food vessel should be black, while any reflector focusing on it should be as near to a mirror as practicable. The box should be insulated, and painted black on the inside as there’s no point in reflecting solar energy back out of the box. The top should be sealed (to retain the heat) so access should be from the side or the back.
Now I just need to invent a selective cloud-dragger which moves them - as Spike Milligan would have said - ‘in the general direction of away’. It’s a funny thing but when you live with solar energy, you tend to notice clouds more.
This is the kind of set-up that lends itself to slow cooking of soups, hotpots and stews during still, clear winter days, brought to us free by a technology which won’t be breaking down anytime soon.
That can’t be too bad. ■